The long-term objective of this research project is to combine cellular and computational approaches in the analysis of information processing in an identified neural network which underlies a well analyzed behavioral response, the siphon withdrawal reflex, in the marine mollusc Aplysia. This simple reflex offers two key advantages for a computational analysis of learning: (1) the reflex exhibits a variety of forms of both non-associative and associative learning; and (2) the neural circuit underlying the reflex is quite well understood. Thus this system provides an excellent opportunity to construct a biologically realistic quantitative model, based on empirically determined cellular properties and synaptic interactions, that can provide important insights into the nature of information processing underlying learning and memory. There are three specific aims of the project: (1) a CELLULAR ANALYSIS will be directed at the detailed neuronal properties and synaptic interactions within the siphon withdrawal network; (2) a COMPUTATIONAL ANALYSIS will be directed at constructing a quantitative model that captures the essential features of information processing in the network; and (3) APPLICATIONS OF THE MODEL will be aimed at a quantitative analysis of specific forms of learning and memory known to be mediated by the network. Information obtained from this project would be of significance (1) from a basic scientific perspective since it could provide valuable insights into the cellular and molecular mechanisms underlying learning and memory; (2) from an applied perspective, since it could help to elucidate general computional principles utilized by a network to generate adaptive modifications (which in turn could facilitate construction of interactive machines capable of goal-directed behavior, for application in both clinical and educational contexts); and (3) from a theoretical perspective, since it could address fundamental questions concerning the nature of adaptive modifications within a computational network that are required for the expression of different forms of learning and memory.